1. Field of the Invention
The present invention relates generally to telephone line concentrator switching systems and, more particularly, to a concentrator system that includes a processor at each end of the concentrator for independent control, at both ends of the concentrator, of switching functions, error checking, and other functions.
2. Description of the Prior Art
Since not all subscribers require service at any one time, there is no need to have an equal number of connections between a group of subscribers and a telephone central office. Line concentrators were therefore developed to concentrate the number of subscriber lines into a lesser number of trunks which would then be extended to the central office. Such an arrangement, however, was found to be cost-competitive compared to in-place cable only for relatively simple line concentrator switching systems.
In the past, line concentrators tended to be large electromechanical devices, requiring a high degree of maintenance, or devices that could operate only using a subscriber carrier or only if a system were connected to a certain type of telephone switching system.
Also, maintenance could not be easily performed at the remote end of the concentrator except on the most expensive of systems, because there was little or no way of checking whether an error correction made by maintenance personnel at the remote unit was effective in eliminating the problem. This is because system fault or malfunction indicators were minimal or nonexistent at the remote unit. In addition, except for the most basic of maintenance routines, any check-out of a line concentrator required the interaction of maintenance personnel to enable the detection of errors and error diagnosis. Often a system had to be taken out of service before such error correction tests could be performed. Only recently have separate monitoring systems been developed to aid in the maintenance of such switching systems. Even these systems, however, have not heretofore been inexpensively incorporated as an integral part of a line concentrator system.
The present invention takes advantage of state-of-the-art microcircuits to create a flexible and powerful line concentrator system that is cost competitive in comparison with the alternative of adding further trunk paths, while allowing substantial improvements in operation over prior concentrator devices to be made. The present invention allows full system check-out to be made, at either the central office unit or the remote unit, of any system faults or errors which have been automatically discovered by the unit. Full control over system operation and access to trouble codes and systems status is available to maintenance personnel at both the central office terminal and at the remote terminal. The invention also provides other unique features in the areas of real-time maintenance of trunks and lines, intercommunication between the central office terminal and remote terminal over idle trunks, and other advantages as described herein. Patents of general interest include U.S. Pat. No. 3,980,839 issued Sept. 14, 1976, a maintenance monitor for telephone switching systems, and U.S. Pat. No. 3,917,908, issued Nov. 4, 1975, a call concentrator control system.